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Why are camera lenses made from several elements instead of one simple lens?

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Diagram showing the negative-positive photographic process: a scene is captured on film in a camera, developed into a negative, projected onto paper with an enlarger, and developed again to produce a positive print. — technology of photography Figure 1: Sequence of negative–positive process, from the photographing of the original scene to enlarged print (see text).

Camera lenses are constructed from multiple elements rather than a single lens because a simple lens produces an imperfect image with various innate defects known as aberrations.12

A single lens often fails to focus light rays into a sharp, clear point, resulting in blurred images, color fringes, or distorted lines. By combining several lens elements—which may vary in shape, material, and separation—designers can ensure that the aberrations produced by one element are counteracted by the opposite aberrations of another.12

Common aberrations addressed by these complex systems include:
* Chromatic aberration: Where different colors of light focus at different planes.3
* Spherical aberration: Where light rays passing through the outer parts of the lens do not meet at the same focus as those passing through the center.3
* Distortion, Coma, and Astigmatism: Various faults that affect image sharpness and geometry.3

The complexity of a lens system increases with the desired aperture size, angle of coverage, and level of precision required.1